Students work at Oak Brook's Brook Forest Elementary School, where nearly every student passed state exams. (Antonio Perez, Chicago Tribune)

A stellar rise in state test scores has won accolades for Mount Prospect's John Jay Elementary School, including an Illinois "Academic Improvement Award" and a recent congratulatory visit from the state school superintendent.

But the celebrated gains at John Jay and at schools across Illinois are likely to recede quickly.

Hundreds of thousands more grade school students could fail the Illinois Standards Achievement Tests next month because of tougher passing requirements, a Tribune analysis has found.

The consequences are certain to startle parents used to seeing their children pass, create a public relations challenge for schools and trigger questions about how prepared students are to move on to junior high, high school, college and work.

As once-impressive passing rates tumble, a less flattering portrait of Illinois schools is certain to emerge, experts say.

"It is causing some controversy. I've been getting some hate mail," said state School Superintendent Christopher Koch, who helped push through the higher passing bar for third- through eighth-graders taking ISATs in math and reading. The State Board of Education approved the changes late last month.

Koch and other educators and researchers agree that the passing threshold on the exams has been too low, given that students should be mastering higher-level skills as they prepare to take new, tougher state exams in 2014-15.

But raising the bar will not be without consequences. If the higher benchmarks had been in place last year, about 365,000 students would have failed the math ISATs and 372,000 would have flunked the reading exams, according to a Tribune analysis.

That's compared with 129,000 students who failed math and 186,000 who failed reading on the 2012 test. About 900,000 students took each of the exams.

The Tribune also found that while 76 to 88 percent of students passed ISATs across all grades, those figures would have plunged to 56 to 62 percent under the new passing requirements.

Scores would have dropped substantially in a broad spectrum of schools and communities. In affluent Naperville, for example, 88 to 96 percent of students passed ISAT exams in District 203. But those passing rates would have dipped to 77 to 82 percent under the tougher passing requirements.

Chicago Public Schools passing rates would have dropped to below 50 percent in most grades, and at the state's largest junior high school, in Cicero, they would have plummeted below 40 percent, according to the Tribune analysis.

Those projected scores are significant, not only because they could predict how schools might score this year but because the reading and math ISATs have been a key barometer for more than a decade of how well students, schools and districts are doing. The exams have helped parents gauge whether their children are performing at least at grade level, or have fallen behind and need extra help.

`A great disservice'

The state tests also are used to judge schools, a cornerstone in efforts to comply with the federal government's No Child Left Behind standards enacted in 2002.

The law requires students from all backgrounds to pass state exams. If too many children fail, schools can face sanctions. In particular, schools with high poverty rates that fail repeatedly have to provide special tutoring, or even let students transfer to better-performing schools.

Establishing lower passing requirements on state exams helped Illinois and other states avoid sanctions over the years. Illinois even lowered the passing requirement on eighth-grade math ISATs in 2006, before Koch took over as state superintendent.

Some educators question whether the lower bar helped or hurt students who were scoring well but may not have been achieving at a level that would prepare them for college and work.

"Perhaps we've been doing these children a great disservice, quite honestly," said retiring Superintendent Sandra Martin, who has been at the helm of DuPage's Butler School District 53 for nearly a decade. The affluent district has focused for years on getting students to attain the highest level of performance on ISATs rather than simply passing the exams, she said.

Passing rates hit 100 percent last year for almost every grade at the district's Brook Forest Elementary School. But that performance would have dipped slightly in most grades had the higher bar been in place in 2012. Third-grade results would have dropped the most, to a 91 percent passing rate in reading and math, the Tribune found.

That's lower than this year's No Child Left Behind requirement — a 92.5 percent passing rate on reading and math ISATs — so even Brook Forest could be challenged to meet the federal standard.

Only about 1 percent of schools will likely meet that 92.5 percent passing standard, the lowest performance ever, according to a review by Advantage Analytics LLC, a consulting company that crunches data for Butler and other school districts.